Photo-electric cell, method of and means for making the same



J. KUNZ.

PHOTO ELECTRIC C ELL, METHOD OF AND MEANS FOR MAKING THE SAME.

Pamnted June 14, 19211 3 SHEE TS-SHEET I.

APPLICATION HLED AUG-24' 1918.

J. KUN'Z.

-PHOTO ELECTRIC CELL, METHOD OF AND MEANS FOR MAKING THE SAME.

APPLICATION FILED Aue 24. 1918.

1,381,474, Patented June 14, 1921.

3 SHEEISSHEET 2.

J. KUNZ. PHOTO ELEC-TRIC CELL, METHOD or AND mrmsfro'a MAKING. THESAME.-

APPLICATION FILED AUGZM I918.

1,381,474. Patented June14, 1921.

3 SHEETS-SHEET 3.

UNITED STATES PATENT OFFICE.

JAKOB KUNZ, 0F UBIBANA, ILLINOIS, ASSIGNOR T0 BOARD OF TRUSTEES OF THEUNIVERSITY OF ILLINOIS, OE URBANA, ILLINOIS, A CORPORATION OF ILLI.

NOIS.

PHOTO-ELECTRIC CELL, METHOD OF AND MEANS FOR MAKING THE SAME.

To all whom it may concern:

Be it known that-I, JAKon KUNZ, a citizen of the United States, residingat Urbana, in the county of Champaign and State of Illinois, haveinvented a certain new and useful Improvement in Photo-Electric Cells,Methods of and Means for Making the Same, of which the following is afull, clear, concise, and exact description, reference being had to theaccompanying drawings, forming Ia part of this specification.

.L y invention relates to photo-electric cells.

I employ as a sensitive element, a suitable alkali metal. The fact thatalkali metals under proper conditions are sensitive to light haspreviously been known.

There has been an increasing demand in various arts for an accurate andsensitive photo-electriccell. Heretofore selenium has been employed butthe selenium cell,at least as heretofore constructed-has not beensufiiciently sensitive, nor are its characteristics suitable for carefulwork.

My invention aims to provide a cell which shall meet this demand. v

I provide an evacuated glass chamber having two electrodes, one of whichconsists of a dense film of an alkali metal in a suitable form andcondition, lying on the inner surface of the chamber. The chamber may befilled with hydrogen or an inert gas, such as nitrogen, argon, helium,or neon or the like. This film electrode is so arranged that the lightto be measured will fall upon the same.

The other electrode is placed in the immediate vicinity of the filmelectrode and is preferably in the form of a screen lying in the path ofthe-enteringl light, but so constructed as to obstruct t e light aslittle as possible. Between these two electrodes there is formed a fieldsubject to and sensitive to the influence of light.

A cell of this type when properly constructed is characterized by greatsensitiveness, uniform sensitiveness over a wide range of lightintensities or impressed voltages, not subject to change by aging,rapidity of action, and as I have found by experiment, a straight linecharacteristic curve.

The human eye is sensitive to light over a range of intensity ofsubstantially from one in 10*, but the cell o y n ent on m ySpecification of Letters Patent. Patented J 14 1921 Application filedAugust 24, 1918.

Serial No. 251,345.

The cell of my invention is more sensi-\ tive to colors than is thehuman eye and can be employed for distinguishing objects of dlfferentcolors such as leaves, glass, silks, etc. It appears that thesensitiveness is greater for short wave lengths, as the cell is moresensitive to blue and ultra violet as well as to Roentgen rays.

I prepare the cell by first depositing a silver mirror in contact withthe shorter electrode. Then I connect the cell to a system of pipes andchambers comprising a pump for evacuating the cell and containmg in oneof the chambers an alkali metal and other chambers various gases reuired. The metal may be any one of the ollow- 1n group:

ithium.

Sodium.

Potassium.

Rubidium.

Ceesium.

The cell is carefully evacuated and then the metal is distilled upon thesilver mirror and in contact with the short electrode, but is carefullykept off of the other electrode. Thereafter, the cell is filled withhydrogen and is subjected to a relatively high electrical potential tocause a glow discharge of electricity. The tube is then pumped out andthereafter filled with argon, nitrogen, neon or other suitable gas, tothe proper degree, and is then sealed off.

In order to'eXplain to those skilled in the art how to construct andpractice my invention, I shall now describe one embodiment thereof inconnection with the accompanying drawings which form a part of thepresent specification.

Figure 1 is a side elevation of a cell embodying my invention;

Fig. 2 is a longitudinal axial section taken on a plane at right anglesto the plane of the sheet in Fig. 1;

Fig. 3 is a diagram illustrating the use of my invention with a sourcecurrent in series with t-he cell;

Fig. lis a similar diagram indicating the use of the cell of myinvention as a wave detector;

Fig. 5 is a diagrammatic layout of the apparatus and method employed informing the cell of my invention; and Fig. 6 is a diagram similar to thediagram of Fig. 4.

The cell comprises a glass bulb 1 having a laterally extending arm 2through which the leading in wire for the screen electrode 3 isintroduced. The bulb 1 has an arm 1 lying upon the opposite side and inline with the arm 2 through which the alkali metal for the filmelectrode 5 is introduced. This leg is also employed for exhausting thebulb 1 and for connecting the same with the various chambers and pipesto be described later. The arm t might very well be dispensed with andcould be sealed oft close to the bulb 1, if desired.

A. leading in wire 6 is disposed in a thickened portion 7 of the sidewalls of the bulb 1. This leading in wire comprises an outer loop 8 andan inner portion which is maintained in contact with the film electrode5. The film electrode 5 comprises a film or surface of an alkali metalwhich in this par-' glass bulb above the line 10 has no coating ofpotassium metal as this portion of the bulb is left clear for theadmission light be measured. The film of alkali metal is backed in thelower portion of the bulb by a silver backing or mirror which lies belowthe line 11 indicated in 1. This silver mirror is first deposited on thewalls of the bulb prior to the distilling of the allrali metal upon thebulb. The silver mirror insures the electrical contact between thealkali film and the leading in wire 6. The screen electrode 3 comprisesa circuring or" metallic wire, in this case silver wire,which ring isprovided with a plurality of cross wires 12 having their ends attachedto the ring and being arranged in criss-cross fashion to form a coarsescreen. The wires 12 are or" very small diameter.

The leading in wire for the screen electrode 3 comprises two sections 13and 14, respectively. The section 13 passes through the end wall 15 ofthe arm 2 with a concentric metal sleeve 16 about the same. Between thewire 13 and the sleeve 16 there is a filling of glass 17 for maintaininga tight closure. lhe wire 13 and the sleeve 16 bre made of platinum asthis metal has substantially the same coeliicient of expansion as glass.

The wire 14 which is joined to the wire 13 might also be of platinum ascould the wire ring 18, but I prefer to employ silver as the same isequally satisfactory and more plentiful. The wire 14 is covered with acoating of glass 19, this coating serving the double purpose ofinsulating the wire 1 and of stiliening the same so as to support thescreen electrode 3 in proper position.

In Figs. 3, at and 6 l have indicated the manner of use of the cell ofmy invention. As shown in Fig. 3, for the measurement of light from thesource L, the photo-electric cell is so placed that light from thesource L will enter the clear space or opening 20 in the bulb 1 of thecell and pass through the screen electrode 3 and tall upon the filmelectrode 5.

The cell is connected in series with an indicator 25 which indicator maybe a very sensitive galvanometer. A suitable source of current, such asa storage battery, and a resistance 27 are connected in series with theell and the indicator 25: The potential of the storage battery may bevaried by an adjustable contact mechanism 28 so that the voltage acrossthe terminals of the cell may be varied from about four volts to 120volts.

have conducted numerous experiments with cells of this type made up withvarious alkali metals and filled with various gases or evacuated only,and l have dis covered that the cell is suitable for measuring purposesin that over a given range the photoelectric. current given oil by thecell is proportional to the intensity of illumination to which the cellis subjected. The cell is useful for photometric purposes, particularlyin investigations in physics having to do with measurement of therel'lection, transmission, radiation and absorption oi light undervarious conditions. The cell is also highly useful in spectroscopy andin astronomy it is particularly useful in the measurement of double starsystems in order to ascertain their radius, mass, density, distance andsurface brightness. Further uses of the cell of my invention are inplant physiology and photochemistry.

For accurate measurement of light for all the above purposes, it ishighly desirable that the cells remain constant, that is, not subject todeterioration or change, and that the response of the cell to the lightaction should be instantaneous and in proportion" to the intensity. Thisl have been able to accomplish by the cell of my invention.

When the cell is in use the platinum cylinder or sleeve 16 is connectedto ground, as

shown at 30 in Fig. 3, in order to discharge any electricity which mayaccumulate on the glass surfaces in the stem or arm 2. 1 consider thisconstruction of the grounded sleeve or cylinder 16 in conjunction withthe terminal 21 to be an important structural feature of my invention.

It is not absolutely essential that a source of current such as 26 beemployed in the circuit of the indicator 25, but I find that theoperation of the system is more satisfacto when such a source isprovided. The indicator 25 may be an electrometer and in that event theresistance 27 is preferably of a. high value of the order of between 10and 10 ohms or higher.

I have found that the cell of my invention is a very sensitive wavedetector for wireless telegraphy and telephony and the like. When thusemployed, the cell is excited by light from the source L, as shown inFig. 4, so that electrons pass from the film electrode 5 to the screenelectrode 3 within the cell. The incoming waves entering by way of theantenna 31 are rectified by the cell and give an indication at theindicator 25 then passing to ground at 32. The source of current 26 maybe omitted. The current operating on the indicator 25 may be amplifiedby an audion or other relay device.

In Fig. 6 I have shown the preferred manner in which I connect the cellfor wave detection. The indicator 82 is a string electrometer, which isconnected to the terminal 21 of the screen electrode 3. The electrometeris connected to ground through the middle point of the battery 83.

The antenna 31 is connected to the film electrode and also throughsuitable connections including the inductance 84 and resistance 85 toground. Suitable capacities 86 and 87 are connected in a manner wellunderstood by those skilled in the art.

I shall now describe one manner in which the cell of my invention may beconstructed. The glass bulb 1 with the screen electrode in place andwith the silver mirror deposited on the lower part of the bulb with thelead-.

ing in wires in place is connected by means of the arm 4 to the systemshown in Fig. 5.

. The arm 4 is connected with the horizontal glass tube which has thebulbs or enlargements 42, 43 and 44 therein. The arm 4 is also providedwith a small depression or cup the purpose of which will be describedlater. The horizontal tube 41 is connected to a vertical tube 45 andthis vertical tube is connected through the stop cocks 46 and 47 to thepump main 53 and thence to a suitable suction pump for exhausting theair from the system.

Between the stop cocks 46 and 47 a plurality of tubes 54, 55 and 56 leadoff to separate chambers. being. controlled by the stop cocks 48, 49 and50, and respectively.

The connecting tube 54 leads oil to a chamber 57 containing palladiumwhich has absorbed a relatively large content of hy drogen. A suitableburner 58 is provided for heating the palladium to cause the same t olvehvdro cn when desired.

The tubeis connected with a bulb or chamber 59 filled with charcoal 60for absorbing and giving off argon, as will be described late For thispurpose, a double walled receptacle 61 containing liquid air 62 isrovided.

he pipe 56 leads to a chamber 81 through a valve 50. This chambercontains phos by a stop cock 51. The chamber 66 is connected through thestop cock 52 with the receptacle 67 which contains argon. The chambersor bulbs 63 and 66 are provided with heating devices such as the burners68 and 69.

The bulb 1 connected to the horizontal tube 41 is surrounded by aheating coil 70 for heating the entire bulb with both arms 2 and 4. Asmallerheating coil, 71 shown in dotted lines in Fig. 5 is provided,this coil being adapted to surround the arm 2 for heating the same, aswill be described later. The electric circuit including the source ofcurrent 26, the galvanometer 25 and resistance 27, is provided forconnection to the terminal of the cell at the proper time, as will bedescribed later. A suitable source of light 73 is also provided fortesting the cell, after the same is nearing completion.

The outer end of the horizontal tube 41 being open, alkali metal, asindicated at 75, is introduced into the bulb 44. The end of the tube isthen sealed at 76. The valves 46-47 are then opened and the valves 48,.49 and 50 are closed and the air pump which is preferably of themercury type is operated to pump the air out of the system.

The initial depositing of the silver mirror upon the bottom of the bulbmay be performed in any of the well known ways, as is understood bythose skilled in the art.

After the air has been pumped out of the system the alkali metal 75 isdistilled from the bulb 44 into the bulb 43 by heating the bulb 44 witha Bunsen burner as shown at 77 and at the same time cooling the bulb 43.It isapparent that any source of heat other than the Bunsen burner maybe employed.

After the air has been pumped out, the heating coil 70 is slipped overthe cell and the entire cell is heated to about 177 centigrade and issubjected to the heat for two or three hours to take out all gases whichmay have been occluded or absorbed in the glass or in any of the partsof the cell. During all this time the air pump 18 in operation to carryaway such gases or vaors.

p The metal which has been distilled in the bulb 43 is now evaporatedtherefrom and distilled in the bulb 4L2. Thereafter, while the pump isstill operating and the beaten, the alkali metal is distilled or pouredinto the enlargement 4.0 in the arm 4 of the cell. The heating coil isthen removed and a smaller heating coil, as shown in dotted lines at 71is placed about the arm 2 which contains the leading in Wire for thescreen electrode 3 and the lower portion of the bulb l which containsthe silver mirror is cooled with water or with ice. A small burner flameis then put below the alkali metalat the point 40 in the stem or arm 4'while the pump is active and while the coil 71 maintains the heat ofsubstantially 150 centigrade upon the arm 2, the interior of the bulbbecomes substantially uniformlycoated with the alkali metal. When: sucha coating has been established, the application of heat at the pointQO-isstopped and the top of the bulb 1 is heated, as indicated by theburner 78 shown in dotted lines, to drive the alkali metal away from thetop of the bulb to form a window for the admission of light. This is tomain tain a clear transparent portion 20 through which the light mayenter the cell. The heating coil 71 prevents the distillation of anymetal in the leg 2 or on the electrode 3. The metal of the electrodeconducts heat from the stem or arm 2 time remaining hot and tending tokeep the alkali metal from. distilling or condensing thereupon.

After the first layer has been distilled upon the interior of the bulb,another layer is deposited in the same manner, and thereafter the clearspace 78 is again heated to drive away the metal vapor. The coating ofalkali metal is applied in about three steps in order to secure auniform layer of the same. The silver mirror tends to maintain aconducting relation between all the particles of the alkali metal whichis in fact deposited in minute droplets but which, when the process ofdistilling is finished, form a continuous layer upon the inside of thecell. It is quite important that the alkali metal be kept out of thestem 2 and off of the positive electrode, otherwise the action of thecell may be interfered with.

Thereafter the valve 47 is closed and with the valvest) and-'50remaining closed and the valve d6 remaining open, the valve- 4:8

is opened. This connects the bulb or chamber 57 to the system. Hydrogenat a pres sure of two or three millimeters is then admitted through thecell, this hydrogen being preferably secured from palladium byheatingthe same. With the hydrogen remaining in the-bulb 1, the source ofcurrent 26 is connected through the terminals of the cell and an.electro-motive force of'about 300 volts is impressed upon the terminalsof-the cell.' A beautiful golden glow which assume is an electricaldischarge, then. occurs in the tube. This potential is employed for onlyprobably other gases may be employed.

When the sensitive film is thus formed I test the cell to ascertain itscondition. For this purpose- I decrease the voltage across the terminalsto about 120 volts and energize the source of light 73. The currentthrough the galvanometer 7 5 is then measured and if the rightsensitiveness has been secured, the operation is then finished.

If the sensitiveness is not high enough the potential is increased toabout 300 volts and the formation of thelayer with hydrogen iscontinued. It is very easy to pass the most sensitive point and if thisoccurs the hydrogen is pumped out and a little more of the alkali metalis distilled, as be fore, and the formation of the film with hydrogenand the electrical discharge is repeated. been secured, the hydrogen ispumped out of the system, the valve 48 being at this time closed and thevalves 46 and 47 open. The valves 47 and 46 are thereafter closed.

The valve 52 is next opened to admit argon from the chamber 67 to thechamber 66. The chamber 66 contains calcium in broken up form and as theargon is admitted to the chamber 66, the calcium is heated with a Bunsenflame or other source of heat, such as electric current. The calciumabsorbs any oxygen and nitrogen which may be contained with the argon.

The valve 51 is next opened and the purifled argon is then passed to thechamber 63 which contains copper oxid. The copper oxid is heated tosubstantially red heat and serves to absorb any hydrogen which may becontained in the stream of argon. The pipe 56 has a chamber 81 in whichis lodged some phosphorous pentoxi'd for absorbing any moisture thatmight be contained in the argon or that mi ht be evolved by heating ofthe copper-0x161. The valve 50 is then opened to admit argon into thesystem between the valves 46 and 47, and after the system issubstantially filled with argon the valve 50 is again closed. The bodyof charcoal 60in the chamber 59is surrounded with a bath of liquid airat 62 and the valve 49 is opened. The argon which is contained in thesystem is then absorbed by the charcoal 60.

When the last trace of argon has been absorbed by the charcoal, thesource of our- When the right sensitiveness has i ar on gas.

rent 26 is connected across the terminals of the cell to impresssubstantially 120 volts across the same through the galvanometer orelectroineter 25. If the body of charcoal 60 does not absorb all of theargon, the same ma be removed by means of the air pump. he valve 46 isthereafter opened and the valve 49 being open, the chamber 61 containingthe liquid air 62 is removed from the bulb 59 and the charcoal 60 beginsto evolve The indicator 25 is then carely watched as the argon isadmitted until the point of maximum deflection is attained. The valve 46is then closed and the cell is ready to be sealed off at the point 8Q.

If neon or helium were employed instead of argon, a suitable containerfor the same would be connected to the system, as indicated by thecontainer 67 which contains argon.

It is not essential that the cell be filled with an inert gas, but Ifind that greater sensitiveness is secured by doing so.

I do not intend to be limited to the precise details of construction oroperation above indicated.

I claim:

1. In combination, a transparent bulb of insulating material, a wirepassing through and sealed in the walls of the bulb, a metallic cylinderconcentric with the wire and extending through and sealed in the wallsof the bulb.

2. In combination, a glass bulb, a wire passing through the walls of thebulb, a metallic cylinder concentric with the wire and extending throughthe wall of the bulb, said wire being connected to a suitable source ofcurrent, and saidmetallic cylinder being connected to round.

3. In combination, a glass vessel having a tube integral with andextending therefrom, a wire passing through the wall of said tube, ametallic cylinder concentric with the wire and extending through thewall of the tube, said wire extending through said tube into the glassvessel and a coating of glass on said wire and forming a tight closurebetween the wire and the cylinder.

4. The method of forming a light sensitive surface in a photo-electriccell which comprises evacuating a glass bulb forming the cell, cooling aportion of the cell externally, introducing the vapor of an alkalinemetal into the bulb to deposit a film of metal upon the inner walls ofthe same and then heating a portion of the cell while another portion isbeing cooled to drive away the alkaline metal from said heated portionto form a transparent portion.

5. In the formation of a photo-electric cell comprising a bulb havin anextendin arm with an electrode in the bulb supporte on a leading-inwire, said wire extending through the arm, the process which comprisesevacuating the bulb and arm, introducing the vapor of an alkaline metalinto the bulb, cooling a portion of the bulb, and

heating the arm to cause heat to be conductprevent deposit of thealkaline metal thereupon, and simultaneously heating a portion of thebulb to form a transparent portion in line with said electrode and theportion which is cooled.

7. The method of depositing a film of alkali metal in a photoelectriccell which comprises cooling a portion of the cell introducing a vaporof the metal to be deposited and heating the portions of the cell uponwhich no film is to be deposited.

8. The method of forming a photo-electric cell which comprisesevacuating the cell, distilling a thin coating of alkali metal upon oneelectrode only, subjecting said coating to an electric discharge in thepresence of hydrogen and then filling the cell with argon and thensealing off the cell.

9. The method of forming a light sensitive film of an alkali metal uponone of the electrodes of a photo-electric cell which comprises fillingthe cell with vapor of the metal, cooling the one electrode to deposit afilm of metal thereupon, and heating the other electrode to prevent thedeposit of the metal thereupon.

10. In combination, a leading-in wire, a glass coating on said wire, acylinder fitting upon and sealed to said glass coating, a glass bulb,said cylinder passlng through and being sealed in the walls of saidbulb, said cylinder being electrically independent of said leading-inwire.

11. In a device of the class described, a closed tube having a pair ofelectrodes within the same. a thin film of a suitable light sensitivemetal in contact with the walls of the tube and forming one electrode,sald thin film lining substantially the entire inner walls of the tubewith the exception of an opening-in line with the other electrode,whereby substantially all extraneous li ht other than that to bemeasured is exclu ed.

12. In a cell of the class described, a closed chamber of substantiallys herical form having an interior coating 0 a light sensitive alkalimetal except for a small portion forming a window, and a flat screenelectrode lying at the center of the chamber and at substantially rightangles to the light rays admitted through the window whereby asubstantially uniform field is formed be tween the coating and thescreen.

13. In a cell of the class described, a bulb having a hollowsubstantially cylindrical arm extending laterally therefrom, anelectrode comprising a metallic ring lying within the bulb with its axisin the direction of the rays of light which act upon the cell, a wireextending from said ring through said arm and terminating outside theWall of the end of the arm, said ring having a plurality of fine wiresconnected thereto to form a screen within the ring, a silver mirrorcoating one side of the bulb, a leading in wire passing through the wallof the bulb and connecting with the silver mirror, and a coating ofsensitized alkali metal deposited upon the silver mirror and upon thewalls of the bulb except a relatively small portion of the bulb in linewith the axis of the ring for the admission of light, said coating ofalkali metal forming a light sensitive electrode and preventing theaccumulation of a static charge upon the walls of the bulb.

14:. In a photo-electric cell, a spherical bulb havinga substantiallycylindrical hollow arm extending laterally therefrom, an-

electrode comprising a metallic ring lying centrally within the bulbwith its axis in'the direction of the rays of light which act upon thecell, a wire extending from said ring through said arm and terminatingoutside the end Wall of the arm, a glass coating upon said wire, ametallic sleeve covering said glass coating where the wire passesthrough the end wall of the arm said sleeve extending beyond the sidesof the end wall of the arm both internally and externally to prevent anycreepage of electricity over either the external or internal walls ofthe bulb between electrodes, a metallic mirror coating one side of thebulb, a leading in wire passing through the side wall of the bulb atsubstantially right angles to the axis of said ring and being inelectrical connection with said mirror, and a plural coating ofsensitized alkali metal deposited upon the silver mirror and the innerwalls of the bulb excepting a small portion of the bulb in line with theaxis of the ring for the admission of light, said coating of alkalimetal forming a light sensitive electrode and preventing theaccumulation of a static charge upon the walls of the bulb.

15. In a device of the class described, a bulb, an electrode in thebulb, a glass stem for the electrode having a wire running therethroughand connected to the electrode, and a metallic coating for the outer endof the stem said bulb forming a seal with the stem on said metalliccoating, a second electrode projecting through a wall of the bulb, saidmetallic coating being interposed between the electrodes to preventsurface creepage of electricity along either the external surface or theinternal surface of the bulb.

16. The method of depositing an alkali metal in a photoelectric cellfrom a vessel which comprises connecting the vessel containing thealkali metal through a plurality of chambers with the -cell, evacuatingthe cell and progressively distilling the alkali metal from the vesselthrough the chambers successively while the cell is being evacuated andfinally into the cell.

17. The method of depositing an alkali metal in a photo-electric cellfrom a vessel, which comprises distilling the metal in a plurality ofsuccessive steps toward and nally into the cell and repeating thedistillation to form a plurality of coatings upon the interior of thecell, said distillation being carried on while the cell is evacuated.

18. In a cell of the class described, a closed. glass bulb having aphoto sensitive interior coating of alkaline metal over the majorportion thereof forming one electrode, and a flat screen electrodeplaced substantially at the center of the bulb and at right angles tothe light admitted to the electrode whereby a substantially uniformfield is formed between the electrodes.

In witness whereof I hereunto subscribe my name this 17 day of Au st1918.

' JA OB KUNZ.

